JP2778801B2 - Exhaust gas treatment catalyst - Google Patents

Description

The present invention relates to an exhaust gas containing nitrogen oxides (hereinafter abbreviated as NOx), carbon monoxide (CO), and hydrocarbons (hereinafter abbreviated as HC). It relates to a catalyst to be purified.

[Conventional technology]

In combustion exhaust gas emitted from gasoline engines such as automobiles, diesel engines such as trucks and buses, etc.
It contains harmful substances, such as NOx, CO, and HC, which are thought to cause photochemical smog. From the viewpoint of environmental protection, the development of a method to remove them is a serious and urgent social issue.

Adsorption method, oxidation absorption method, NOx removal method in exhaust gas,
Although there is a catalytic reduction method, etc., a catalytic reduction method that does not require a post-treatment is considered to be economically and technically advantageous. In this catalytic reduction method, NOx is passed through the catalyst in the presence of a reducing gas.
Is converted into harmless nitrogen, which can be divided into two methods depending on the type of reducing agent.

That is, a so-called specific selective reduction method in which a reducing gas such as hydrogen, carbon monoxide, or a hydrocarbon is added and brought into contact with a catalyst, and a so-called selective reduction method in which a reducing gas such as ammonia is added and brought into contact with a catalyst. The former has the disadvantage that a large amount of reducing agent is required because the NOx removal reaction proceeds after the reaction of oxygen and the reducing agent coexisting in the gas, but carbon monoxide and carbonized carbon dioxide, such as exhaust gas generated from internal combustion engines such as automobiles. If a reducing agent such as hydrogen is already contained in an equimolar amount or more of oxygen, it is advantageous to purify NOx in exhaust gas by the non-selective reduction method. Is being put to practical use.

In the case of using no catalyst, automobile exhaust gas shows the gas composition as shown in Fig. 1. However, ternary materials such as Pt, Rh (active metal body) / Al ₂ O ₃ (carrier) / cordierite (honeycomb base material) When a catalyst is used, the gas composition becomes as shown in FIG. 2, and three components of NOx, CO, and HC are purified near the stoichiometric air-fuel ratio. The engine fuel exhaust gas at the stoichiometric air-fuel ratio has substantially the following composition.

CO: 0.3~1.0%, NO: 0.05~0.15 %, H 2 O: about _{13%, H 2: 0.1~0.3%} , HC: 0.03~0.08%, SO 2: about
0.002%, O ₂ : 0.2 to 0.5%, CO ₂ : about 12% [Problems to be Solved by the Invention] The three-way catalyst as described above, which has been put to practical use for purifying exhaust gas from automobile engines, is used. In this case, oxygen is consumed by the oxidation reaction, and the NO reduction reaction proceeds in a state where the oxygen concentration is considerably low. Therefore, the current three-way catalyst is effective only near the stoichiometric air-fuel ratio (14.6), and it is difficult to reduce NOx in a high air-fuel ratio region where the combustion consumption rate can be reduced.

On the other hand, in order to improve fuel efficiency,
There is a need to be able to reduce and remove NOx, and the emergence of a catalyst capable of denitration at a wide range of O ₂ concentrations has been awaited.

In recent years, it has been reported that a catalyst obtained by ion-exchanging Cu with silica gel or zeolite is effective for direct decomposition of NO (Japanese Patent Application Laid-Open No. 60-125250). However, when this catalyst is used as it is as a catalyst for purifying exhaust gas of an automobile engine, the combustion of CO and HC is remarkable, so that there is a problem that reduction and removal of NOx do not proceed so much and heat resistance is poor.

[Means for solving the problem]

An object of the present invention is to solve the above-mentioned problems of the prior art, and a catalyst in which copper and a specific active metal are further contained by using a crystalline silicate having a specific composition and a crystal structure. Found that NOx, CO, and HC decreased even in the region near the stoichiometric air-fuel ratio and higher than the stoichiometric air-fuel ratio, that is, in the state where a large amount of oxygen was present, and completed the present invention.

That is, the present invention relates to (1) having the X-ray diffraction characteristics shown in Table A below, and expressed as a molar ratio of oxides in a dehydrated state, (1.0 ± 0.8) R ₂ O · [aM ₂ O ₃・ bAl ₂ O ₃ ] ・ ySiO ₂ (However,
In the above formula, R is an alkali metal ion and / or hydrogen, M
Is one or more element ions selected from the group consisting of group VIII metals, rare earth metals, titanium, vanadium, chromium, niobium, antimony, and gallium, a + b = 1, a ≧ 0, b ≧ 0, y> 1
1) An exhaust gas treatment catalyst comprising a crystalline silicate having the chemical formula 1) and copper and a specific active metal coexisting.

(2) The specific active metal is magnesium, calcium, barium, strontium, lithium, sodium, potassium, boron, aluminum, phosphorus, tin, antimony, silicon, titanium, zinc, vanadium,
The exhaust gas treatment catalyst according to (1), which is at least one selected from niobium, iron, cobalt, nickel, manganese, lanthanum, cerium, praseodymium, neodymium, samarium, and tungsten.

It is.

[Action]

Regarding the action of the catalyst used in the present invention, the oxidation-reduction cycle (Cu ²⁺ Cu ⁺ ) of ion-exchanged copper ions is easy, oxygen is easily released at a relatively low temperature, and the copper on the crystalline silica silicate is CO or CO. These activated gases react with NO to activate HC and remove NOx. Furthermore, the coexistence of copper and another metal improves the heat resistance of the active metal (copper), thereby improving the selectivity of the denitration reaction.

That is, the metal has an action of suppressing sintering of Cu at a high temperature while maintaining the NO adsorption ability and the oxidation-reduction cycle ability of Cu ions, and magnesium (M
g), calcium (Ca), barium (Ba), strontium (Sr), lithium (Li), sodium (Na), potassium (K), boron (B), aluminum (Al), phosphorus (P), tin ( Sn), antimony (Sb), silicon (S
i), titanium (Ti), zinc (Zn), vanadium (V), niobium (Nb), iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), lanthanum (La), cerium ( Ce), praseodymium (Pr), neodymium (N
d), at least one of masarium (Sm) and tungsten (W).

These metals can be supported on a crystalline silicate having a specific crystal structure and a specific composition by an ion exchange method, and can coexist with copper. Furthermore, various salts of nitrates, chlorides and sulfates can be supported on the carrier by an impregnation method.

The preferred content of copper and other metals supported on the carrier made of the specific crystalline silicate used in the present invention is the carrier.
0.2 to 30 parts by weight, preferably 0.4 to 2 parts by weight, of Cu per 100 parts by weight
0 parts by weight, on the other hand, as other metals, Mg, Ca, Ba, Sr, Li, Na,
K, B, Al, P, Si, Sn: 0.2 to 8 parts by weight, Sb, Ti, Zn, V, Nb, Fe, C
o, Ni, Mn, La, Ce, Pr, Nd, Sm, and W are 0.1 to 6 parts by weight.

The crystalline silicate used in the present invention is a silica source, a group VIII element, a rare earth element, a titanium, vanadium, chromium, niobium, antimony, gallium oxide source, an alumina source, an alkali source, water and It is synthesized by making a reaction mixture containing the organic nitrogen-containing compound and heating the mixture for a time and at a temperature to produce a crystalline silicate.

Further, the crystalline silicate used in the present invention is SiO ₂ / A
l ₂ O ₃ high silica zeolite with a ratio of 12 or moreAl, a part of Al in the structure of the conventional zeolite is a group VIII element, a rare earth element,
It replaces titanium, vanadium, chromium, niobium, antimony, and gallium, and further contains SiO ₂ / (M ₂ O ₃
+ Al ₂ O ₃ ) ratio of 12 or more, and is produced from a reaction mixture having the following molar composition.

SiO ₂ / (M ₂ O ₃ + Al ₂ O ₃ ) 12 to 3000 (preferably 20 to 200) OH ⁻ / SiO ₂ 0 to 1.0 (preferably 0.2 to 0.8) H ₂ O / SiO _{2 2 to} 1000 (preferably Is 10 to 200) Organic nitrogen-containing compound / (M ₂ O ₃ + Al ₂ O ₃ ) (preferably 5 to 50) When the catalyst used in the present invention is used industrially, it is formed into an appropriate shape. It is desirable to use. For example, silica, inorganic oxides such as alumina or clay as a binder, optionally using a molding aid such as an organic material, spherical,
It is formed into a column shape and a honeycomb shape. The catalyst used in the present invention can be regarded as a catalyst used in the present invention even if a crystalline silicate before carrying copper and another metal is preliminarily molded and the molded body is exchanged with copper ions. The size of the compact is not particularly limited.

Example 1 A crystalline silicate was synthesized as follows.

Water glass, ferric sulfate, aluminum sulfate, and water were mixed in a molar ratio of Na ₂ O · (0.1Fe ₂ O ₃ · 0.9Al ₂ O ₃ ) · 30SiO ₂ · 1600H ₂ O, and sulfuric acid was added. Is added in an appropriate amount,
After the pH of the above mixture was adjusted to about 9, propylamine and propyl bromide were added as organic nitrogen-containing compounds to Fe ₂ O.
₃ , Add 20 times the total number of moles of Al ₂ O ₃ and mix well, 500cc
Into a stainless steel autoclave.

The mixture was reacted at 160 ° C. for 3 days while stirring at about 500 rpm. After cooling, the solid content was filtered, washed thoroughly with water until the pH of the washing water was about 8, dried at 110 ° C for 12 hours,
Calcination was performed at 3 ° C. for 3 hours.

The crystal grain size of this product is about 1 μm, and the composition expressed by the molar ratio of oxide is expressed in the form of dehydration (H, N
a) ₂ O · (0.1Fe ₂ O ₃ 0.9Al ₂ O ₃ ) · 30SiO ₂ This is called crystalline silicate 1.

When synthesizing this crystalline silicate 1, hydrochloric acid or the like may be used instead of sulfuric acid among the raw materials, ferric chloride may be used instead of ferric sulfate, and silica sol may be used instead of water glass. A similar silicate was obtained by using.

The same silicate was obtained by reacting at 170 ° C. or 180 ° C. for 2 days instead of reacting at 160 ° C. for 3 days as hydrothermal synthesis conditions.

Crystalline silicate 1 was prepared in the same manner as in crystalline silicate 1 except that the amounts of ferric sulfate and aluminum sulfate added during the preparation of the raw material of crystalline silicate 1 were changed as shown in Table 1 in terms of the molar ratio of Fe ₂ O ₃ to Al ₂ O _3. Crystal silicates 2 to 4 were prepared by repeating the same operation as in the above case.

In preparing the crystalline silicate 1, hydrochloric acid was used instead of sulfuric acid, and instead of ferric sulfate, cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride, chromium chloride, Antimony chloride and gallium chloride in oxide equivalent
Crystal silicates 5 to 14 were prepared by repeating the same operation as for crystalline silicate 1 except that the same mole number as Fe ₂ O ₃ was added. The composition of these crystalline silicates excluding the organic nitrogen-containing compound is represented by the molar ratio of oxides (dehydrated form), and is expressed as (H, Na) ₂ O · (0.1M ₂ O ₃ 0.9Al ₂ O ₃ )・ 30SiO ₂
Met. Where M is Co, Ru, Rh, La, Ce, Ti, V, Cr, Sb, Ga
(Numerical order of crystalline silicates 5 to 14).

In the crystalline silicate 1, SiO ₂ /(0.1
Fe ₂ O ₃ +0.9 Al ₂ O ₃ ) Except that the ratio was 20,80, the same operation as that of the crystalline silicate 1 was repeated, and each of the crystalline silicates 1
5,16 were prepared.

It was confirmed that the powder X-ray diffraction patterns of the above crystalline silicates 1 to 16 showed the patterns shown in Table 1.

An ion exchange operation was performed in which 10 g of each of the above crystalline silicates 1 to 16 was placed in an aqueous solution in which 1 g of cupric chloride and 1 g of zinc chloride were dissolved in 500 cc of water and stirred at room temperature for 12 hours. After repeating this ion exchange operation three times, the resultant was washed with water and dried at 100 ° C. for 12 hours to prepare Catalysts 1 to 16 (corresponding to the number of crystalline silicate).

Further, 110 g of the crystalline silicate was replaced with cupric chloride (CuC
and _{l 2 · 2H 2 O) 1g} , instead of zinc chloride (ZnCl _2), calcium chloride _{(CuCl 2 · H 2 O)} , barium chloride (BaCl ₂ · 2H
₂ O), strontium chloride (SrCl ₂ .6H ₂ O), sodium chloride (NaCl), potassium chloride (KCl), boric acid (H ₃ B
O ₃ ), aluminum chloride (AlCl ₃ ), tin chloride (SnCl ₂
2H ₂ O) and silicon tetrachloride (SiCl ₄ ) were placed in an aqueous solution in which 1 g of each was dissolved in 500 cc of water, and an ion exchange operation was performed by stirring at room temperature for 12 hours. After repeating this ion exchange operation three times, the resultant was washed with water and dried at 100 ° C. for 12 hours to prepare Catalysts 17 to 25.

In addition, cupric chloride (CuCl ₂ ) was added to 10 g of the crystalline silicate.
2H ₂ O), antimony chloride (SbCl ₃ ), titanium tetrachloride (TiCl ₄ ), vanadium trichloride (VCl ₃ ), niobium chloride (N
Bcl _5), iron trichloride (FeCl _3), cobalt chloride (CoCl ₂ · 6H
₂ O), nickel chloride _{(NiCl 2 · 6H 2 O)} , manganese chloride (M
nCl ₂ · 4H ₂ O), lanthanum chloride (LaCl _3), cerium chloride (CeCl _3), chloride praseodymium _{(PrCl 3 · 7H 2 O)} , neodymium chloride (NdCl _3), samarium chloride (SmCl _3), tungsten chloride ( Each aqueous solution of WCl ₆ ) is mixed with the above crystalline silicate at an atomic ratio of Cu 0.6 mmol / g,
The catalyst was impregnated so as to carry ol / g and dried at 110 ° C. for 24 hours to prepare Catalysts 26 to 39.

Catalysts 1 to 39 were sized to 16 to 32 mesh, and 0.5 g of the catalyst was charged into a normal-pressure fixed-bed flow reactor, and an activity evaluation test was performed under the following reaction conditions. The results are also shown in Table 2.

Although some of the catalysts in Table 2 have (H, Na) ₂ O remaining, the description is omitted for convenience and only the basic skeleton is shown.

Gas _{composition: NO: 500ppm, C 3 H} 6: 500ppm, CO: 0.5%, O 2: 2%, He
Balance gas flow rate: 2 Nl / h, reaction temperature: 500 ° C [Comparative Example 1] 10 g of the crystalline silicate 1 described in Example 1 was put into an aqueous solution in which 1 g of cupric chloride was dissolved in 500 cc of water, and an ion exchange operation in which stirring was repeated three times at room temperature for 12 hours was performed. .
After the ion exchange, the catalyst was washed with water and dried at 100 ° C. for 12 hours to prepare a catalyst 40.

This catalyst 40 was subjected to an activity evaluation test under the same conditions as those described in Example 1. The results are shown in Table 2.

Example 2 0.5 g of the catalyst 1 of Example 1 and the catalyst 40 of Comparative Example 1 were charged into a fixed-bed flow reactor under normal pressure, and an activity evaluation test was conducted by changing the reaction conditions. Table 3 shows the results.

The activity evaluation result after 100 hours shown in Table 3 is 730 ° C. ×
It is an activity evaluation result performed after a 100-hour (gas composition atmosphere) forced heating test.

As described above, it has been found that the catalyst used in the present invention has high activity even when a gas containing SO ₂ is used, and the change in activity with time is small.

Example 3 A mixture of ferric chloride and chromium chloride was used in place of ferric sulfate at the time of preparing the raw material of the crystalline silicate 1 of Example 1, and Na ₂ O · (0.09Fe ₂ O ₃ · 0.01Cr ₂ O ₃・ 0.9Al ₂ O ₃ ) ・ 30Si
Except that it was prepared to have a molar ratio of O ₂・ 1600H ₂ O,
Crystalline silicate was obtained in the same manner as in crystalline silicate 1, and co-ion exchange of Cu and Zn was performed in the same manner to obtain catalyst 41.

In addition, a co-ion exchange of Cu, Zn, and Mg was performed using the crystalline silicate 1 in the same manner as in Example 1, and the catalyst was used.
I got 42. Table 2 shows the results of the same activity evaluation as in Example 1.
Are shown together.

〔The invention's effect〕

As described above, in the present invention, NOx, CO, and HC are reduced by using a catalyst in which copper and a specific metal are further contained in a crystalline silicate having a specific crystal structure and a specific composition in the present invention. It is possible to reduce NOx, CO, and HC in the contained exhaust gas.

In this example, the activity evaluation test was performed on the present catalyst in the form of granules. However, it is needless to say that the present catalyst is coated on a honeycomb base material such as cordurite to have an effective action even in a honeycomb shape.

[Brief description of the drawings]

FIG. 1 is a chart of the composition of an automobile exhaust gas (without a catalyst), and FIG. 2 is a chart of an exhaust gas composition when a three-way catalyst is used.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Yoshiaki Obayashi, Inventor 4-62-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (72) Inventor Seito Suwa 4 Kannon-Shimmachi, Nishi-ku, Hiroshima-shi, Hiroshima No.6-22, Mitsubishi Heavy Industries, Ltd. Hiroshima Laboratory (58) Fields investigated (Int. Cl. ⁶ , DB name) B01J 21/00-38/74 C01B 33/20

Claims (2)

(57) [Claims] 1. It has an X-ray diffraction characteristic shown in the following Table A,
In the dehydrated state, represented by the molar ratio of the oxide,
(1.0 ± 0.8) R ₂ O ・ [aM ₂ O ₃・ bAl ₂ O ₃ ] ・ ySiO ₂ (However,
In the above formula, R is an alkali metal ion and / or hydrogen, M
Is one or more element ions selected from the group consisting of group VIII metals, rare earth metals, titanium, vanadium, chromium, niobium, antimony, and gallium, a + b = 1, a ≧ 0, b ≧ 0, y> 1
An exhaust gas treatment catalyst comprising a crystalline silicate having the chemical formula (1) and copper and a specific active metal coexisting. 2. The specific active metal is magnesium, calcium, barium, strontium, lithium, sodium, potassium, boron, aluminum, phosphorus, tin,
2. The method according to claim 1, wherein the antimony is at least one selected from the group consisting of antimony, silicon, titanium, zinc, vanadium, niobium, iron, cobalt, nickel, manganese, lanthanum, cerium, praseodymium, neodymium, masalium, and tungsten. Exhaust gas treatment catalyst.